In data processing systems, magnetic disc drives are often used as storage devices. In such devices, read/write heads located on a slider (or an air bearing) are used to write data on or read data from an adjacently rotating disc. The head is located either above or under the disc and isolated therefrom by a thin film of air. The thickness of the thin film of air depends on the disc's rotational speed and the shape of the air bearing surface. During drive operations, the fly height of the head continuously changes as the head pitches and rolls with the varying topography of the disc. If the quality of the disc or the read/write head is poor, occasional rubbing or sharp contact may occur between the disc and the head. Such contact may damage the head or the disc, which can cause a loss of valuable data.
To efficiently accommodate changes in disc data storage characteristics (i.e., ever-narrowing recording track widths and increases in linear magnetic recording density), the head fly height (or slider clearance) is progressively being decreased. These decreases in fly height can cause the contact frequency between disc and head to increase. To prevent damage to either the disc or head for such low slider clearance, it has been recognized that the surface of the disc should be very flat and free of bumps.
As the head/disc interface of the magnetic hard drive approaches the near-contact region, the number of the thermal asperities (TA's) detected by the magnetic heads is quickly rising to an unmanageable level. These thermal asperities not only render recording tracks unusable for data recording, but also degrade the magnetic heads and potentially could fail the entire drive. A thermal asperity results from the strong interaction between a flying head and a defect on the disc surface. The interaction can be either contact or non-contact as long as it induces a sudden change in the head/media spacing. Hence, reducing media defects is a key to ensuring good reliability of magnetic hard drives.
One procedure that has been used to flatten disc surfaces is a two-step glide/burnish process. Within such a process, a glide head is first flown over the disc surface to detect and record asperities high enough to potentially strike a flying read/write head and cause data errors or head crashes. The glide head typically includes an advanced air bearing (AAB) surface designed to enable a particularly low fly height that is lower than most read/write heads fly during normal conditions.
After the glide step is completed, a burnished sweep is performed to remove recorded asperities. The burnish sweep consists of actually contacting the asperities with burnish pads located on an air bearing surface of a flying burnish head, thereby leveling the height to a desired specification. The glide and burnish steps can be repeated to ensure all asperities have been properly reduced or removed.
Traditionally, the burnish head does not include an AAB surface design, resulting in large variances in fly height. Variations in the burnish step can ultimately lead to a decrease in data yield efficiency. However, a burnish head that includes a complex AAB surface and an inefficient configuration of burnish pads can also lead to yield loss.
Because of the tight fly control required for the glide process in the flight variation typical of the burnish head air bearing surface, the traditional burnish head is not suitable to be also used as a glide head. Thus, the glide/burnish process has relied on a lengthy two head process. Each switch between the glide and burnish steps requires use of a separate head.
The objective of the burnishing is to remove the loose and soft particles and asperities, cut defects and asperities and condition the media surfaces. However, the deteriorating wear and scratch resistance of the media surface due to thinning overcoats makes the surface more prone to particle imbedding. Therefore, there is a need for burnish heads to incorporate particle/surface contamination clearing air bearing stability (ABS) features for high performance magnetic media.
Traditional burnishing heads with waffle or elliptical types consist of discrete pads distributed over an entire air bearing surface. Due to the discrete nature of such pads, the heads lack the flying stability and show a large head-to-head variation in fly height, which makes it difficult or impossible to fine tune the aggressiveness of the media burnishing. In addition, such designs lack ABS features for complete and finishing wipes.
A traditional burnish arrangement is depicted in FIG. 1, and lacks a completeness in the wiping action. Because of it, loose particles and surface contamination can easily escape burnishing rails especially in the cases of faster disc rotation and head speed. Such a head burnishing imposes a hard limit to production tests that is proportional to rotation speed and seeking rate. In addition, the conventional design lacks aggressiveness in asperity cutting and surface conditioning. During a burnishing action, the asperities and surface contaminations are encountered by a relatively gradual ABS surface. Also, as will be described with FIGS. 2A-2C, such head burnishing lacks a particle deflection, thereby increasing the likelihood of particle embedding.
FIG. 1 depicts a conventional arrangement 10 in which a disc 12 is mounted on a disc rotational mechanism. The disc 12 is rotated in the rotational direction indicated by arrow 32.
During burnishing operations, an arm 14 is moved with a seeking velocity, indicated by arrow 26. The arm 14 is translated at the seeking velocity by a translation mechanism (not shown in FIG. 1). The arm 14 has a first end 16 and a second end 18. At the second end 18 a burnishing head 20 is mounted and has a gradual ABS surface (not shown).
The disc 12 may be considered to have a diameter 24 to which a central longitudinal axis 28 of the arm 14 is parallel. The central longitudinal axis 21 of the burnishing head 20 is aligned with the central longitudinal axis 28 of the arm 14. The arm axis 28 and the burnishing head axis 21 are parallel to the diameter 24 of the disc 12. With a non-skewed design, such as depicted in conventional arrangement 10 of FIG. 1, during a sweeping operation the arm axis 28 and the burnishing head axis 21 are maintained substantially parallel to the diameter 24 of the disc 12. The asperities and particles 30 are swept by the burnishing head 20 during the burnishing process.
FIG. 2A shows the bottom surface of a burnishing head 20. The leading edge 34 is a tapered edge, as better seen in FIGS. 2B and 2C. Rails 22, provided as air bearing surfaces, exhibit the tapered front edge 34. The gradual air bearing surface, such as that depicted in FIGS. 2A-2C cause a particle 30 that is encountered to become embedded by contact with the burnishing head 20. Since the parallel configuration (i.e., “non-skewed” configuration”) does not provide for particle deflection, there is an increased likelihood of particle embedding. The conventional non-skewed head burnish design lacks a complete wiping action so that loose particles and surface contamination can easily escape the burnishing rails, especially in cases of disc rotation and head sweep. This poses a limitation to production tests that is proportional to rotation speed and seeking rate.